The cs coat color mutation has been further studied. We have been able to exclude all known mutants on C with the exception of Cch. In previous crosses with Cch, an expected additional class was observed but the tester stock carried b and, thus, the progeny segregated for alleles of C on a Bb background which made interpretation difficult. The F/St strain is a short-lived mouse with a high incidence of spontaneous leukemia. A (C57xF/St)F2 hybrid was used to make a B10.F congenic which is also short-lived but has low leukemia. In our colony, C57Ha were used to make a C57.F congenic using only C57Ha female at each step in backcrossing. Our C57.F are long lived. To date, 21 new congenic lines of mice have been derived from recombination between T (Brachyury) and H-2 on chromosome 17. Two of these lines separate the locus controlling quantitative variation in glyoxalase I activity (Qglo-1) from the H-2 complex and, thus, represent the first T-H-2 region congenics in non-t chromosomes with defined donor segment inserts. Several other strains define a new H-2-restricted CML target antigen, which preliminary results indicate may map very close to the classical T (Brachyury) gene. The genetics of this locus is currently top priority. A survey of genomic DNA of these 21 new strains with H-2 cDNA probes has failed to define any H-2-associated restriction fragment length polymorphism (RFLP) to the left of the classically defined H-2K gene with four restriction enzymes. We have also produced what may be a "self-immunization" type of monoclonal antibody. Strain distributions have been done with this antibody by cytotoxicity. Our objectives for the coming year are to continue investigations in the following areas: (1)\probing the flanking genes of H-2 on chromosome 17; (2)\explore the immunoregulatory role of the peptide in in vitro tests; (3)\analysis of probable mutants at the phenotypic and at the gene level; and (4)\the specificity of binding and lysis to SV40 and other virally transformed cells.